In recent years, a standard referred to as DVI standard has been established for transmitting video data to a video display device in a format of digital data when a video signal source such as a television tuner, a video player or a personal computer device body, and a video display device such as a monitor receiver are connected.
Details of the DVI standard will be given in following descriptions of embodiments while, to be brief, the DVI standard allows video data to be transmitted to the display device by digitizing primary color signals R, G and B in pixel units, respectively, thereby transmitting and displaying high-definition images. In addition, as the video data in pixel units are transmitted, a display driver can be directly driven by the received video data on the display device side, thereby realizing display or the like with a relatively simple processing configuration.
Data transmitted through a cable that is defined by the DVI standard are fundamentally only video data, and thus when considering that audio data are transmitted at the same time, the display device and an audio output device such as a tuner must be connected through an audio cable, which is different from the cable defined by the DVI standard.
However, when the display device and the signal sources are connected through plural cables, the connection configuration is adversely complicated.
More specifically, when considering a configuration of the system that transmits only video data, for example a video signal source 701 and a display device 703 are connected through a DVI standard cable 702 as shown in FIG. 7, and video data which are coded according to the DVI standard are transmitted through the cable 702, whereby the video data can be transmitted from the video signal source 701 to the display device 703. On the other hand, when video data and audio data are transmitted from a video/audio signal source 801 to a display device with speaker 804 as shown in FIG. 8, the signal source and the speaker display must be connected so that the video data are transmitted by a DVI standard cable 802 and the audio data are transmitted by an audio signal cable 803 that is different from the cable 802. When the video/audio signal source 801 and the display device 804 are connected as shown in FIG. 8, video that is outputted from the signal source 801 can be displayed on the display device 804, and sounds can be outputted from speakers 805L and 805R which are mounted on the display device 804.
However, when video data and audio data are transmitted using different cables as shown in FIG. 8, the connection configuration is complicated correspondingly. It is preferable that the devices are connected through as few cables as possible.
The technology for multiplexing video and audio data, and transmitting multiplexed data through one cable can be realized by adopting a data transmission technique that employs for example a bus line which is standardized as IEEE (The Institute of Electrical and Electronics Engineers) 1394 system. However, quite complicated data processing is required to transmit data through the bus line according to this IEEE 1394 system, and accordingly a quite large circuit construction is needed as a configuration for an encoding process to transmit data on the transmitting end, or a configuration for decoding data that are received through the bus line on a receiving end, resulting in a high cost. Further, in the IEEE 1394 system, the video data and audio data are compressively coded and multiplexed in view of a transmission rate and the like, and thus the image quality is inferior to that in the case where video data digitized in pixel units are transmitted according to the above-mentioned DVI standard.
In addition, when the digitized audio data are to be transmitted together, a video clock and an audio clock must be transmitted simultaneously, so that signal lines for the transmission are needed, and jitter is unfavorably increased because the high-speed signals are transmitted.
The present invention is made to solve the above-mentioned problems, and this invention has for its object to provide a data transmission method and a data receiving method by which audio data can be transmitted easily and satisfactorily using an existing interface through which video data are transmitted.